The prevalence of obesity has increased throughout the United States with one in three Americans categorized as obese. Fewer than a quarter of Americans who attempt to lose weight actually follow current recommendations of increasing exercise and reducing caloric intake. Those who attempt losing weight through regular aerobic training by using a treadmill or elliptical often get bored and lose motivation very quickly, leading to decreased exercise adherence. An exercise program that has grown in popularity over the past few years as an alternative to traditional endurance and resistance training is known as CrossFit.
CrossFit was introduced in 2001 by its founder Greg Glassman and is considered “one of the fastest growing sports in America” with over 13,000 gyms worldwide. CrossFit is a high-intensity power training (HIPT) type of exercise that consists of a combination of gymnastics, plyometrics, functional movements, anaerobic intervals, weightlifting, sprinting and Olympic lifting. These constantly varied exercises, which are combined into the “Workout of the Day” (WOD), allow for training in all three human energy systems: the creatine phosphate (CP) system, anaerobic glycolysis, and oxidative phosphorylation and can be adapted for all levels of age and fitness.
The majority of CrossFit participants include men and women ranging from 19-60 years old, looking to improve all aspects of health and fitness with a desire to lose weight and increase performance. A popular approach to weight loss that has gained recognition in recent years is the low-carbohydrate ketogenic diet (LCKD). This diet is classified by a decrease in carbohydrates with a subsequent increase in proportions of dietary fat and protein.
The reduction in carbohydrates, usually below 50 grams per day, allows a shift from glucose to fat-based metabolism  which produces water-soluble ketone bodies known as acetoacetate (AcAC), 3-β-hydroxybutyrate (3HB) and acetone. Ketone body formation, also known as ketogenesis, has been shown to aid in the treatment of several diseases such as refractory pediatric epilepsy, cardiovascular disease, Type 2 diabetes, and obesity. In addition, ketogenic diets are recognized as one of the more effective treatments for improvements in body weight, body composition, fasting serum lipid levels, and diet tolerability, especially when compared to low-fat diets.
Although there are many benefits to following a LCKD, there has been much controversy surrounding its relationship to exercise performance. While there is a paucity of literature, some studies have reported favorable outcomes in body weight and body fat reductions when following a LCKD and adhering to either an endurance or resistance type training protocol. To date, there have been no published investigations supporting changes in body composition or performance in response to a HIPT type exercise program such as CrossFit, while adhering to a LCKD.
The purpose of this study is to determine if consuming a 6-week LCKD and participating in a CrossFit training regimen yields significant improvements in body composition while maintaining or increasing performance. Specifically, we hypothesized that a LCKD would be a successful fat loss and weight loss strategy for CrossFit participants while maintaining or improving performance. Our second hypothesis was that those participating in CrossFit training while adhering to their usual dietary intakes would show significant increases in performance with minimal decreases in body mass or body fat content.